The piezoelectric speaker generally includes a frame, a diaphragm fixed on the frame with bonding material, and a piezoelectric element attached on the diaphragm.
A piezoelectric speaker as known is used to convert electrical energy into mechanical energy. When AC power is applied to the piezoelectric speaker, a piezoelectric element deforms and drives a diaphragm closed attached thereto to vibrate so as to compress air for producing sounds.
Sound pressure level (SPL) and total harmonic distortion (THD) are the important characteristics of a piezoelectric speaker. The sound pressure is the local pressure deviation from the ambient atmospheric pressure, caused by a sound wave. The total harmonic distortion is a measurement of the harmonic distortion present and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.
In general, as the piezoelectric element in the piezoelectric speaker vibrates, the energy will waste partially from the piezoelectric element transfer to the frame through the diaphragm and the bonding material which result in a smaller sound pressure level.
Furthermore, the fixed frame of the piezoelectric speaker is easier to cause ripple because of the resonance phenomena of mechanical structure. When a mechanical resonance occurs in the speaker, vibrations arise in a fundamental frequency and its multiples; thereby a sound pressure produced by the speaker would increase in resonance frequency bands and the sound pressure decreases while a distortion increases in non-resonance frequency bands.
Thus, the target of the researchers is to provide a piezoelectric speaker with high sound pressure, low distortion, wide range and a flat sound pressure curvature.
Therefore, how to overcome the above-described drawbacks has become urgent.